1. Field of the Invention
The present invention relates to a compound-eye imaging device.
2. Description of the Related Art
A compound-eye imaging device is known which comprises an optical lens array having multiple micro optical lenses arranged in a matrix of rows and columns, and a solid-state imaging element (photodetector array) for imaging multiple unit images of a target object which are formed by the respective optical lenses of the optical lens array so as to reconstruct the multiple unit images into a reconstructed image (refer to e.g. Japanese Laid-open Patent Publication 2001-61109). FIG. 9 is a schematic perspective view of a part of such conventional compound-eye imaging device 100.
As shown in FIG. 9, the compound-eye imaging device 100 has an optical lens array 101 and a solid-state imaging element 102 as well as a partitioning wall 103 placed between the optical lens array 101 and the solid-state imaging element 102 so as to allow lights collected by respective optical lenses L11, L12 . . . L33 to reach the solid-state imaging element 102 without interference therebetween, thereby forming high definition images by the respective optical lenses L11, L12 . . . L33, making it possible to obtain a high definition reconstructed image. In the following description, the combination of one optical lens (e.g. optical lens L31) with an area of the solid-state imaging element 102 to image a unit image formed by the one optical lens will be referred to as imaging unit U as shown by the double-dot dashed line in FIG. 9.
Here, a mechanism to allow a compound-eye imaging device to form a high definition reconstructed image from multiple unit images will be explained with reference to FIG. 9. In the compound-eye imaging device 100, the optical lenses L11, L12 . . . L33 are distributed on the optical lens array 101 in a matrix of rows and columns, so that the respective unit images formed on the solid-state image element 102 are images which are viewed at angles slightly different from one another relative to the target object (i.e. images with parallax). By using unit images which are thus slightly different from one another to have slightly different information, it is possible to form a reconstructed image based on the larger amount of information, making it possible for the reconstructed image to have a higher definition than that of each unit image.
However, in the compound-eye imaging device 100 described above, the optical lenses L11, L12 . . . L33 are regularly arranged at a constant distance or interval, so that the unit images formed by the optical lenses L11, L12 . . . L33 may in some cases be substantially the same as each other, if, for example, the target object is positioned at a predetermined distance from the compound-eye imaging device 100 as described later, or if the target object is indefinitely far from the compound-eye imaging device. In such cases, the amount of information used to form a reconstructed image decreases, preventing the reconstructed image from having a higher definition than that of each unit image.
The case where the unit images formed by the optical lenses are substantially the same will be described with reference to FIGS. 10A and 10B. FIG. 10A is a schematic side view of the compound-eye imaging device 100, placed vertically, in a mode of collecting lights from a target object T by the optical lenses L11, L12 . . . L33, in which the target object T is positioned in front of, and at a predetermined distance from, the compound-eye imaging device 100. FIG. 10B is a schematic enlarged side view of a portion of FIG. 10A as indicated by the dashed circle 10B. In FIG. 10B, the three optical lenses L11, L21 and L31 in the leftmost column of FIG. 9 are shown, in which the solid-state imaging element 102 is assumed to have 8 (eight) pixels for each of the optical lenses L11, L21 and L31.
Both FIG. 10A and FIG. 10B show light traces of lights collected by the respective optical lenses L11, L21 and L31 to reach the respective pixels of the solid-state imaging element 102, in which such light traces for the optical lenses L11, L21 and L31 are shown by solid lines, coarse dashed lines and fine dashed lines in order from top to bottom. More specifically, in the case of the optical lens L11, for example, the uppermost light denoted by h1 passes through the optical lens L11, and is collected onto the lowermost pixel denoted by g8. Similarly, the n-th light from the top which can be designated by hn passes through the optical lens L11, and is collected onto the (9−n)th pixel from the top which can be denoted by g(9−1). The lowermost light denoted by h8 passes through the optical lens L11, and is collected onto the uppermost pixel denoted by g1. Using the definition above, the combinations of the optical lens L11, L21 and L31 with corresponding areas of the solid-state imaging element 102 to image unit images formed by the optical lenses L11, L21 and L31 can be referred to as imaging units U11, U21 and U31, respectively, as shown in FIG. 10B.
Now, assuming that the target object T is positioned in front of, and at a predetermined distance, from the compound-eye imaging device 100, FIGS. 10A and 10B show the case where light from a point P1 on the target object T is collected by the optical lens L11 as light h2 and imaged by pixel g7 in the imaging unit U11, and is at the same time collected by the optical lens L31 as light h1 and imaged by pixel g8 in the imaging unit U31. Thus, the image of the point P1 imaged by the pixel g7 in the imaging unit U11 is the same as the image of the point P1 imaged by the pixel g8 in the imaging unit U31. This indicates that points on the target object T where the light traces h1, h2, h3 . . . intersect, that are P1, P2, P3 . . . , can be imaged as the same image by different imaging units U.
Thus, it is understood that the conventional compound-eye imaging device 100 with regularly arranged optical lenses (L11, L12 . . . L33) has a plane, which can be referred to as imaginary plane, where the intersection points between light traces (h1, h2, h3 . . . ) are present and concentrated, and that substantially the same unit images are formed when a target object (T) is present on the imaginary plane. Further, referring to FIG. 10A, in addition to the imaginary plane in the position of the target object T, but also another imaginary plane where intersection points between the light traces h1, h2, h3 . . . are concentrated is present in the position shown by the vertical double-dot dashed line a, for example.
Besides, in some cases, it may be required to obtain the distance from a compound-eye imaging device to a target object. However, this is not possible in the case of the compound-eye imaging device 100 with regularly arranged optical lenses (L11, L12 . . . L33), because, as shown in FIG. 10A, when the target object T is far from the image capture device 100, the light traces h1, h2, h3 . . . h8 of lights collected onto the optical lenses L11, L21 and L31 are substantially parallel to each other, so that the unit images imaged by all the imaging units U become substantially the same without parallax, making it impossible to obtain the required distance of the target object T.
Referring back to the first problem, in order to solve the problem of the reduction in the definition of a reconstructed image when a target object is indefinitely far, a compound-eye imaging device is known having imaging units of optical lenses and corresponding areas of a solid-state imaging element, in which the imaging units are adjusted in the position of the optical lenses and the solid-state imaging element such that the positional relationship between an optical lens and a corresponding area of the solid-state imaging element in an imaging unit is slightly offset from that in an adjacent imaging unit. Such a compound-eye imaging device is disclosed, for example, in Japanese Laid-open Patent Publication 2004-146619. However, such compound-eye imaging device does not sufficiently improve the definition of a reconstructed image.
More specifically, in the compound-eye imaging device disclosed in e.g. Japanese Laid-open Patent Publication 2004-146619, the optical lenses are regularly arranged in a matrix of rows and columns on one plane, while the solid-state imaging element has pixels successively offset slightly in the direction parallel to the one plane relative to the corresponding optical lenses. This offset positional relationship may, to a certain extent, reduce the probability that different imaging units form the same image from light from one same point on a target object, as compared to the case where the positional relationship among the optical lenses and the solid-state imaging element is constant. However, the regularity in the arrangement of the optical lenses prevents a significant reduction of such probability.